“The warm and wide-ranging conversation, lasting over an hour, covered how the Center will showcase the South Side of Chicago to the world,” Kensington Palace said in one of several photos it tweeted from the visit.

The warm and wide-ranging conversation, lasting over an hour, covered how the Center will showcase the South Side of Chicago to the world. pic.twitter.com/84lQfvF9iH

A statement from the former first lady’s communication director added that the center also strives to show “the importance of young people staying inspired and hopeful, and the transformative power of students using their voices to change the world."

Obama later thanked "my friend Prince Harry" in a tweet for joining her at the school.

Obama's friendship with Prince Harry runs deep, going back to when her husband served as president. The pair loved surprising people back then, too. The former first lady, who made support for veterans and their families a focal point during her White House years, surprised guests at a 2013 White House Mother's Day tea for U.S. service members by introducing Prince Harry to the crowd.

Obama also has has been a strong supporter of the Invictus Games, the Paralympic-type competition Harry created for wounded warriors. The former first lady joined the prince last year when Orlando, Florida, hosted the Games, and again last month, when the Games were held in Toronto, Canada.

Both Michelle and Barack Obama also share a warm relationship with Harry's brother, Prince William. Indeed, the Obamas paid a visit to Kensington Palace last year that was memorably captured in a meeting with a then 2-year-old Prince George wearing a very adorable bathrobe.